The present invention relates to a developing agent used in, for example, an electrophotographic apparatus, a method for measuring the free component content of the additive to the developing agent, and a method of evaluating the developing agent.
Various assumptions are made with respect to the filming generation in a developing agent. The presence of free silica that is not attached to the toner is considered to be one of the causes of the filming generation.
For example, where the mixing ratio of silica is unduly large, or where the additive mixing conditions are not appropriate, some of the silica particles are present in a free state separated from the toner particles. As a result, the free silica particles are attached to the carrier particles or attached to and deposited on the inner wall of the developing device, on the developing sleeve, regulating blade, etc. It is then considered that the frictional charging properties of the toner are impaired so as to make it difficult to impart an appropriate charging amount to the toner and so as to promote the filming generation.
The attached state of the additive was analyzed in the past by observation with a scanning electron microscope (SEM), transmitting electron microscope (TEM) or the like. However, these methods are dependent on the visual sensation and the analytical result is not quantitative and, thus, is vague in a large proportion.